Here we draw attention to a candidate system with one hot Jupiter and one small, nearby companion, revealed by the recent Kepler data release (DR25). The hot Jupiter, Kepler-730b, has radius Rp=11.36+1.14−0.98 R⊕ and orbital period P=6.492 d, and the newly discovered companion, KOI-929.02, has Rp=1.45+0.15−0.20 R⊕ and P=2.852 d. No transit timing variation (TTV) was detected because of the marginal detection of the small companion transit, but this small companion passed all the validation tests. This system is probably another planetary system with hot Jupiter and small, nearby companion, after the outstanding WASP-47 system, and so far the only such system (out of 46) in the prime Kepler mission. The nature of this system, if confirmed, would suggest that hot Jupiters with small, nearby companions are probably more common than we used to believe. There remains a possibility that the small companion actually transits a star that is different from the hot Jupiter host, and follow-up observations with 10-m telescopes can potentially resolve this issue.

Last edited by Sirius_Alpha on 22nd December 2018, 11:34 am; edited 1 time in total

Kepler-730 is a planetary system hosting a statistically validated hot Jupiter in a 6.49-day orbit and an additional transiting candidate in a 2.85-day orbit. We use spectroscopic radial velocities from the APOGEE-2N instrument, Robo-AO contrast curves, and Gaia distance estimates to statistically validate the planetary nature of the additional Earth-sized candidate. We perform astrophysical false positive probability calculations for the candidate using the available Kepler data and bolster the statistical validation by using radial velocity data to exclude a family of possible binary star solutions. Using a radius estimate for the primary star derived from stellar models, we compute radii of 1.100+0.047−0.050 RJup and 0.140±0.012 RJup (1.57±0.13 R⊕) for Kepler-730b and Kepler-730c, respectively. Kepler-730 is only the second compact system hosting a hot Jupiter with an inner, transiting planet.